Influence of Condensing Temperature On Refrigerating Capacity

In a manner similar to that used to explore the effect of evaporating temperatures on the refrigeration capacity, the influence of condensing temperatures can be examined. Equation 4.7 once again becomes the tool, and all the terms change as the condensing temperature varies with the exception of the specific volume entering the compressor, νs, which is a function of the evaporating temperature only. For the compressor whose volumetric efficiency is shown in Figure 4.2, the effect of condensing temperature on the refrigerating capacity for an evaporating temperature of -10°C (14°F) is shown in Figure 4.9.

Effect of condensing temperature on the refrigerating capacity of an 8-cylinder ammonia compressor with a displacement rate of 0.123 m3/s (260 cfm) operating with an evaporating temperature of -10°C (14°F).

The refrigerating capacity always decreases as the condensing temperature increases, so the measures that are discussed in Chapter 7 on condensers are potential tools to keep the condensing temperature low. Compared to the influence of the evaporating temperature, each degree change in the condensing temperature affects the refrigerating capacity to a lesser extent than a degree change in evaporating temperature. The reason for this difference is that changes in the evaporating temperature also exert a considerable effect on the specific volume entering the compressor, while the condensing temperature does not.

The comparison of the influences of evaporating and condensing temperatures on the refrigerating capacity also appears on the complete map of refrigeration capacity, as shown in Figure 4.10, as controlled by the evaporating and condensing temperatures.

Effect of both the evaporating and condensing temperatures on refrigeration capacity for the 8-cylinder ammonia compressor.

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